
/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "ares_setup.h"

#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#include <arpa/nameser.h>
#else
#include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif

#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"

#ifndef T_OPT
#define T_OPT 41 /* EDNS0 option (meta-RR) */
#endif

/* Header format, from RFC 1035:
 *                                  1  1  1  1  1  1
 *    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                      ID                       |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |QR|   Opcode  |AA|TC|RD|RA|   Z    |   RCODE   |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                    QDCOUNT                    |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                    ANCOUNT                    |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                    NSCOUNT                    |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                    ARCOUNT                    |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *
 * AA, TC, RA, and RCODE are only set in responses.  Brief description
 * of the remaining fields:
 *      ID      Identifier to match responses with queries
 *      QR      Query (0) or response (1)
 *      Opcode  For our purposes, always QUERY
 *      RD      Recursion desired
 *      Z       Reserved (zero)
 *      QDCOUNT Number of queries
 *      ANCOUNT Number of answers
 *      NSCOUNT Number of name server records
 *      ARCOUNT Number of additional records
 *
 * Question format, from RFC 1035:
 *                                  1  1  1  1  1  1
 *    0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                                               |
 *  /                     QNAME                     /
 *  /                                               /
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                     QTYPE                     |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *  |                     QCLASS                    |
 *  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
 *
 * The query name is encoded as a series of labels, each represented
 * as a one-byte length (maximum 63) followed by the text of the
 * label.  The list is terminated by a label of length zero (which can
 * be thought of as the root domain).
 */

int ares_create_query(const char* name, int dnsclass, int type,
    unsigned short id, int rd, unsigned char** bufp,
    int* buflenp, int max_udp_size)
{
    size_t len;
    unsigned char* q;
    const char* p;
    size_t buflen;
    unsigned char* buf;

    /* Set our results early, in case we bail out early with an error. */
    *buflenp = 0;
    *bufp = NULL;

    /* Allocate a memory area for the maximum size this packet might need. +2
   * is for the length byte and zero termination if no dots or ecscaping is
   * used.
   */
    len = strlen(name) + 2 + HFIXEDSZ + QFIXEDSZ + (max_udp_size ? EDNSFIXEDSZ : 0);
    buf = ares_malloc(len);
    if (!buf)
        return ARES_ENOMEM;

    /* Set up the header. */
    q = buf;
    memset(q, 0, HFIXEDSZ);
    DNS_HEADER_SET_QID(q, id);
    DNS_HEADER_SET_OPCODE(q, QUERY);
    if (rd) {
        DNS_HEADER_SET_RD(q, 1);
    } else {
        DNS_HEADER_SET_RD(q, 0);
    }
    DNS_HEADER_SET_QDCOUNT(q, 1);

    if (max_udp_size) {
        DNS_HEADER_SET_ARCOUNT(q, 1);
    }

    /* A name of "." is a screw case for the loop below, so adjust it. */
    if (strcmp(name, ".") == 0)
        name++;

    /* Start writing out the name after the header. */
    q += HFIXEDSZ;
    while (*name) {
        if (*name == '.') {
            free(buf);
            return ARES_EBADNAME;
        }

        /* Count the number of bytes in this label. */
        len = 0;
        for (p = name; *p && *p != '.'; p++) {
            if (*p == '\\' && *(p + 1) != 0)
                p++;
            len++;
        }
        if (len > MAXLABEL) {
            free(buf);
            return ARES_EBADNAME;
        }

        /* Encode the length and copy the data. */
        *q++ = (unsigned char)len;
        for (p = name; *p && *p != '.'; p++) {
            if (*p == '\\' && *(p + 1) != 0)
                p++;
            *q++ = *p;
        }

        /* Go to the next label and repeat, unless we hit the end. */
        if (!*p)
            break;
        name = p + 1;
    }

    /* Add the zero-length label at the end. */
    *q++ = 0;

    /* Finish off the question with the type and class. */
    DNS_QUESTION_SET_TYPE(q, type);
    DNS_QUESTION_SET_CLASS(q, dnsclass);

    q += QFIXEDSZ;
    if (max_udp_size) {
        memset(q, 0, EDNSFIXEDSZ);
        q++;
        DNS_RR_SET_TYPE(q, T_OPT);
        DNS_RR_SET_CLASS(q, max_udp_size);
        q += (EDNSFIXEDSZ - 1);
    }
    buflen = (q - buf);

    /* Reject names that are longer than the maximum of 255 bytes that's
   * specified in RFC 1035 ("To simplify implementations, the total length of
   * a domain name (i.e., label octets and label length octets) is restricted
   * to 255 octets or less."). */
    if (buflen > (MAXCDNAME + HFIXEDSZ + QFIXEDSZ + (max_udp_size ? EDNSFIXEDSZ : 0))) {
        free(buf);
        return ARES_EBADNAME;
    }

    /* we know this fits in an int at this point */
    *buflenp = (int)buflen;
    *bufp = buf;

    return ARES_SUCCESS;
}
